Method for strengthening soils and operating vehicle usable in the method

ABSTRACT

A method for strengthening soils comprising: a step of making in the soil ( 1 ) a hole ( 2 ) that has a main line of extension which is at least mainly vertical;  5  a driving step wherein a micro-pile ( 11 ) is driven into the soil ( 1 ) at the hole ( 2 ); and a step of filling the hole ( 2 ) with a solidifiable material or with a compactable solid granular material; wherein the step of making the hole ( 2 ) in the soil ( 1 ) comprises an inserting step wherein a punch ( 4 ) is inserted in the soil ( 1 ) by applying a pressure to the punch, the punch comprising a lower tip ( 5 ) insertable in the soil ( 1 ), a top portion ( 6 ) opposite to the lower tip ( 5 ), an axis of extension that extends between the top portion ( 6 ) and the lower tip ( 5 ) and a cross-section that increases along the axis of extension going away from the lower tip ( 5 ), and  5  wherein the step of inserting the punch ( 4 ) in the soil ( 1 ) also causes compression and compacting of the soil ( 1 ) surrounding the hole ( 2 ).

This invention relates first to a method for strengthening soils, andsecond to an operating vehicle suitably developed so that it is usablein the strengthening method.

Specifically, this invention may be used for strengthening soils onwhich foundations or pavements already stand (both inside buildings, andoutside such as yards, roads and motorways) and soils on whichfoundations or pavements must subsequently be built.

In the former case, the strengthening work becomes necessary when thesoil yields after the foundation or pavement has already been built,whilst in the latter case the strengthening generally has a preventativefunction, to avoid subsequent yielding in the case of soils which arenot compact and/or settled enough.

At present, strengthening techniques may be based on only injectingexpanding resins or concrete into the soil, or on making resin orconcrete piles, or driving piles and micro-piles to which thefoundations or pavements are then anchored, or on mixed techniques.

Although, at least in some conditions of use, each of these techniquesmay give good results, there is still a great need in the sector forobtaining ever-increasing load-bearing capacities in the soil, and/orgreater load-bearing capacities with less effort in terms of times andcosts.

In this context the technical purpose which forms the basis of thisinvention is to provide a method for strengthening soils which overcomesthe above-mentioned disadvantages.

Specifically, it is the technical purpose of this invention to provide amethod for strengthening soils which allows a high load-bearing capacityof the soil to be obtained in a fast, simple way.

A further technical purpose of this invention is to make an operatingvehicle with which to be able to perform several main steps of themethod according to this invention.

The technical purpose specified and the aims indicated are substantiallyachieved by a method for strengthening soils and by an operating vehicleusable in the strengthening method, as described in the appended claims.

Further features and the advantages of this invention are more apparentin the detailed description, with reference to the accompanying drawingswhich illustrate several preferred, non-limiting embodiments of a methodfor strengthening soils and of an operating vehicle usable in thestrengthening method, in which:

FIG. 1 is a schematic side view of an operating vehicle made inaccordance with this invention which is about to begin a first step ofthe strengthening method;

FIG. 2 shows the operating vehicle of FIG. 1 during the making of a holein the soil;

FIG. 3 shows the operating vehicle of FIG. 2 at the moment when it hascompleted making the hole in the soil;

FIG. 4 shows the operating vehicle of FIG. 3 after it has extracted fromthe soil a punch belonging to the vehicle with which it previously madethe hole in the soil;

FIG. 5 shows the hole in the soil of FIG. 4 after it has been filledwith a filling material according to a first embodiment of thestrengthening method according to this invention;

FIG. 6 shows the result of repeatedly performing the strengtheningmethod at a plurality of adjacent zones of the soil to be strengthened;

FIG. 7 shows the operating vehicle of FIG. 4 while it performs asubsequent step of driving a micro-pile into the soil at the hole in thesoil, according to a second embodiment of the method according to thisinvention; and

FIG. 8 shows the hole in the soil of FIG. 7 after completion of drivingof the micro-pile, and after the hole has been filled with a fillingmaterial according to the second embodiment of the strengthening methodaccording to this invention.

Hereinafter the strengthening method according to this invention will bedescribed, followed by a description of the operating vehicle providedfor use in that method. However, it shall be understood that what isdescribed below, relative to the method and to the vehicle respectively,shall also be applicable to the vehicle and to the method respectively,if technically compatible.

Similarly to other prior art strengthening methods, the method accordingto this invention also comprises two main steps, a step of making a hole2 in the soil 1 and a step of filling the hole 2 with a filling material3. The step of making the hole 2 in the soil 1 is performed in such away that the hole 2 has a main line of extension which is at leastmainly vertical, whilst the step of filling the hole 2 may be performedwith a solidifiable material (such as concrete, resins or bituminousmacadam).

According to a first innovative aspect of this invention, the step ofmaking the hole 2 in the soil 1 comprises making a hole 2 with across-section, transversal to the main line of extension, that decreasesfrom top to bottom; in other words, once completed, the hole 2advantageously has a hopper or funnel shape.

Furthermore, according to a second innovative aspect of this invention,the hole 2 in the soil 1 is obtained by means of what may be consideredactually punching the soil 1. In fact, advantageously, the step ofmaking the hole 2 in the soil 1 comprises an inserting step, wherein asuitably shaped punch 4 is inserted in the soil 1. That punch 4 has alower tip 5 insertable in the soil 1, a top portion 6 opposite to thelower tip 5, and an axis of extension that extends between the topportion 6 and the lower tip 5. The punch 4 also has a cross-section thatincreases along the axis of extension going away from the lower tip 5.Specifically, according to a first embodiment, the punch 4 has across-section which, going away from the lower tip 5, continuouslyincreases along the axis of extension (the punch 4 may, for example,have the shape of a cone or inverted pyramid or, preferably, may befrustoconical or frustopyramidal). However, according to the preferredembodiment illustrated in the accompanying figures, the punch 4 has aplurality of stretches 7 with constant cross-section (for example,cylindrical or parallelepipeds) or increasing cross-section (forexample, frustoconical or frustopyramidal) which are aligned along theaxis of extension, where the cross-section of each stretch 7 is greaterthan the cross-sections of the stretches 7 closer to the lower tip 5 andis less than the cross-sections of the stretches 7 further from thelower tip 5. Advantageously, the difference in cross-section between twoadjacent stretches 7 is in any case small.

The inserting step is also carried out by positioning the axis ofextension of the punch 4 substantially parallel to the main line ofextension of the hole 2 to be obtained (that is to say, vertical).

Thanks to the shape of the punch 4, the step of inserting the punch 4 inthe soil 1 causes compression and compacting of the soil 1 surroundingthe hole 2.

In the preferred embodiment the step of inserting the punch 4 in thesoil 1 is performed without removing material from the soil 1. Despitethat, it is also possible that the step of inserting the punch 4 in thesoil 1 is preceded by a step of making a pilot hole in the soil 1 (wherethe pilot hole will be smaller than the hole 2 to be made) and that thestep of inserting the punch 4 in the soil 1 is performed by insertingthe punch 4 in the pilot hole in order to widen it.

Preferably, the step of inserting the punch 4 in the soil 1 is performedin such a way as to bring the lower tip 5 of the punch 4 to a depth ofat least 2 m, advantageously, at least 3 m (although lesser or greaterdriving depths are in any case possible).

According to the preferred embodiment of this invention, the step ofinserting the punch 4 in the soil 1 is performed by applying pressure,using a first actuating device 8 which is fixed to a first ballastedbody 9. Specifically, in the accompanying figures, the first ballastedbody 9, which acts as a reaction element for the force applied to thepunch 4, is constituted of the rest of the operating vehicle 10described below.

According to the simplest embodiment of this invention, illustrated inFIGS. 5 and 6, once insertion of the punch 4 in the soil 1 has beencompleted the punch 4 is extracted and the hole 2, which is therebyfreed, is filled with the solidifiable filling material 3; then once thelatter has solidified the compacting of the soil 1 may be consideredcompleted. By repeating the same steps a plurality of times, withsuitable spacing, it is also possible to strengthen soils of any extent.

In other words, what is obtained at the end of the method describedabove is one or more wedge-shaped elements (which may or may not be in asingle block—FIG. 6), inserted in the soil 1 and which keep the soil 1surrounding them compressed and compacted.

In contrast, according to a more complex embodiment (to be used, forexample, where higher load-bearing capacities are necessary), onceinsertion of the punch 4 in the soil 1 has been completed, the punch 4is extracted and before the step of filling the hole 2, a driving stepis carried out, during which a foundation micro-pile 11 is driven intothe soil 1 at the hole 2, and, preferably, at the bottom of it (FIG. 7).In other words, the micro-pile 11 is driven into the soil 1 whichsurrounds the hole 2, starting from the hole 2 itself. Advantageously,the micro-pile 11 is driven into the soil 1 with its longitudinal axissubstantially coinciding with the main line of extension of the hole 2.

In the known way, the micro-pile 11 may be constituted of multiple shortmodules (for example, 1 m long), connectable to one another end-on untilthey cover the entire driving depth, which may be more or less deep.

In the preferred embodiment the step of driving the micro-pile 11 isperformed by applying pressure, using a second actuating device 12 whichis fixed to a second ballasted body 13. In the accompanying figures inwhich the second actuating device 12 is also mounted on the operatingvehicle 10, the second ballasted body 13 is constituted of the operatingvehicle 10 itself. Depending on the chosen embodiments, during thedriving step the micro-pile 11 may always be kept with same angularorientation, or it may be made to rotate about its own longitudinal axisthereby achieving pressing—rotating driving of the micro-pile 11 intothe soil 1.

Driving of the micro-pile 11 into the soil 1 is completed when thedesired depth has been reached and, preferably, when the upper portion14 of the micro-pile 11 is positioned inside the hole 2 (advantageouslythe top of the pile is substantially aligned with the treadable surfaceof the soil 1).

At that point, the step of filling the hole 2 may take place, embeddingthe upper portion 14 of the micro-pile 11 positioned inside the hole 2;however, in this case it will be necessary to use a material able toadhere to the micro-pile 11, preferably able to adhere to the micro-pile11 in such a way as to constitute with it substantially a single body;advantageously, this comprises the use of concrete.

In order to improve the adhesion between the micro-pile 11 and thefilling material 3 the upper portion 14 of the micro-pile 11 may havesurface working which increases its roughness (at macroscopic ormicroscopic level) and adhesion capacity, plus projecting elements areconnected to it which will then be set in the filling material 3. Forexample, the surface of the micro-pile 11 may have a plurality ofaxially spaced annular grooves.

FIG. 8 shows the end result achieved once the material has solidified.In this case too, the method may be repeated a plurality of times, withappropriate spacing, to strengthen soils of any extent.

As already indicated in the above description, according to thisinvention an operating vehicle 10 usable in the strengthening method hasalso been provided, whose use is particularly advantageous in the casein which driving micro-piles using pressure is also involved.

The vehicle comprises a chassis 15 on which a movement system for movingthe vehicle on the soil 1 is mounted. The movement system may be eitherof the passive type (e.g.: simple wheels or tracks 16 for making theoperating vehicle 10 a carriage to be towed), or of the active type(which, in addition to wheels or tracks 16 also has an engine 17connected to them).

Mounted on the operating vehicle 10 are at least one driving apparatus18 for driving a micro-pile into the soil 1 and at least one punchingdevice 19 for punching the soil 1 in order to make a hole 2 in the soil1. Optionally, there may also be a second driving apparatus for drivinga second micro-pile into the soil 1, preferably activatable alternatingwith the first driving apparatus 18.

Advantageously, on the vehicle there are also ballasts 20 to make itheavy enough to allow it to act as a reaction element for the forcesapplied to the punch 4 and to the micro-piles. The overall weight of theoperating vehicle 10 with the ballasts 20 must have a centre of gravitysuch as to guarantee the correct reaction force to the punching device19 and to the driving apparatus 18, also taking into account the leverarms which may form in use. In the preferred embodiment the drivingapparatus 18 (or the driving apparatuses if there is more than one) ispositioned at a central portion of the operating vehicle 10, whilst thepunching device 19 is mounted cantilever-style at the front or rear sideof the vehicle. However, other layouts are also possible.

In more detail, the punching device 19 comprises a first member 21, asecond member 22 and a first actuating device 8 which is mounted betweenthe first member 21 and the second member 22 for moving the secondmember 22 relative to the first member 21.

The first member 21 is constrained to the chassis 15 and is constitutedof a rigid arm in the accompanying figures. In contrast, the secondmember 22 is movable relative to the first member 21 between a firstposition and a second position along a punching line, and has the shapeof a punch 4. The second member 22 also has an axis of extension whichextends between a lower tip 5, insertable in the soil 1, and a topportion 6. According to this invention, the second member 22 has across-section which increases along the axis of extension (from thelower tip 5 towards the top portion 6).

The movement of the second member 22 relative to the first member 21 isof the reciprocating type and comprises an outward stroke and a returnstroke. The outward stroke goes from the first position (FIG. 1) towardsthe second position (FIG. 3), and during it the first actuating device 8pushes the second member 22 towards the soil 1, whilst the return strokegoes from the second position towards the first position and during itthe second member 22 is moved away from the soil 1. During the outwardstroke the first actuating device 8 applies a force on the second member22 along the driving line; thanks to its shape with (upwardly)increasing cross-section, the second member 22 is configured to apply tothe soil 1, according to a line of action which is radial relative tothe line of insertion, a portion of the force which it receives from thefirst actuating device 8.

In turn, each driving apparatus 18 comprises a third member 23 which isconstrained to the chassis 15, a fourth member 25 which is movablerelative to the third member 23 between a first position and a secondposition along the driving line, and a second actuating device 12 formoving the fourth member 25 relative to the third member 23.

The movement of the fourth member 25 also comprises an outward strokeand a return stroke. On the outward stroke the fourth member 25 goestowards the second position and the second actuating device 12 pushesthe fourth member 25 towards the soil 1, whilst during the return strokethe fourth member 25 goes towards the first position, and is moved awayfrom the soil 1. During the outward stroke, the second actuating device12 applies a force on the fourth member 25 along the driving line, aforce which the fourth member 25 is configured to transmit practicallyentirely to the micro-pile to be driven in.

As can easily be inferred from the structural description above, in usethe operating vehicle 10 can always be used to make the hole 2 in thesoil 1. If micro-pile 11 driving is also required, the operating vehicle10 can simply be moved until the second actuating device 12 is at thehole 2.

This invention brings important advantages.

Specifically, the fact that it makes the hole in the soil using a punchwhich has a cross-section increasing upwards allows the hole to be madeat extremely low cost, and local compacting of the soil surrounding thehole, thereby significantly increasing the load-bearing capacity of thesoil.

By combining hole making and filling with micro-pile driving at the samehole, it makes it possible to either further increase the load-bearingcapacity of the soil or to obtain load-bearing capacities similar tothose obtainable with only micro-piles, but using significantly shorterpiles.

Last but not least, the operating vehicle according to this inventionmakes the strengthening method applicable in almost any work context.

Finally, it should be noticed that this invention is relatively easy toproduce and that even the cost linked to implementing the invention isnot very high. The invention described above may be modified and adaptedin several ways without thereby departing from the scope of theinventive concept.

All details may be substituted with other technically equivalentelements and the materials used, as well as the shapes and dimensions ofthe various components, may vary according to requirements.

1. A method for strengthening soils comprising: a step of making in thesoil (1) a hole (2) that has a main line of extension which is at leastmainly vertical; and a step of filling the hole (2) with a solidifiablematerial; wherein the step of making the hole (2) in the soil (1)comprises making a hole (2) with a cross-section transversal to the mainline of extension, that decreases from top to bottom, and wherein thestep of making the hole (2) in the soil (1) comprises an inserting stepwherein a punch (4) is inserted in the soil (1) by applying a pressureto the punch, the punch comprising a lower tip (5) insertable in thesoil (1), a top portion (6) opposite to the lower tip (5), an axis ofextension that extends between the top portion (6) and the lower tip (5)and a cross-section that increases along the axis of extension goingaway from the lower tip (5), wherein the inserting step is performed bypositioning the axis of extension of the punch (4) substantiallyparallel to the main line of extension of the hole (2) to be obtained,and wherein the step of inserting the punch (4) in the soil (1) alsocauses compression and compacting of the soil (1) surrounding the hole(2); characterised in that it also comprises, after the step of making ahole (2) in the soil (1) and before the step of filling the hole (2), adriving step wherein a micro-pile (11) is driven into the soil (1) atthe hole (2).
 2. The method according to claim 1, characterised in thatthe step of inserting the punch (4) in the soil (1) is performed withoutremoving material from the soil (1).
 3. The method according to claim 1,characterised in that the step of inserting the punch (4) in the soil(1) is preceded by a step of making a pilot hole in the soil (1) whichis smaller than the hole (2) to be made and in that the step ofinserting the punch (4) in the soil (1) is performed by inserting thepunch (4) in the pilot hole in order to widen it.
 4. The methodaccording to claim 1, characterised in that the step of inserting thepunch (4) in the soil (1) is performed by applying pressure, using afirst actuating device (8) that is fixed to a first ballasted body (9).5. The method according to claim 1, characterised in that the step ofinserting the punch (4) in the soil (1) is performed using a punch (4)with a cross-section that, going away from the lower tip (5),continuously increases along the axis of extension or a punch (4) havinga plurality of stretches (7) with constant cross-section that arealigned along the axis of extension where the cross-section of eachstretch (7) is greater than cross-sections of the stretches (7) closerto the lower tip (5) and is less than cross-sections of the stretches(7) further from the lower tip (5).
 6. The method according to claim 1,characterised in that the micro-pile (11) is driven into the soil (1)with its longitudinal axis substantially coinciding with the main lineof extension of the hole (2).
 7. The method according to claim 1,characterised in that the step of filling the hole (2) is performed byembedding an upper portion (14) of the micro-pile (11) positioned insidethe hole (2) and using a solidifiable material.
 8. The method accordingto claim 1, characterised in that the step of driving the micro-pile(11) is performed by applying pressure, using a second actuating device(12) that is fixed to a second ballasted body (13).
 9. The methodaccording to claim 8, characterised in that during the driving step themicro-pile (11) is also made to rotate about its own longitudinal axisthereby achieving pressing-rotating driving of the micro-pile (11) intothe soil (1).
 10. The method according to claim 1, characterised in thatthe step of inserting the punch (4) in the soil (1) is performed in sucha way as to bring the lower tip (5) of the punch (4) to a depth of atleast 2 m.
 11. An operating vehicle usable in the method according toclaim 1, comprising: a chassis (15); a movement system for moving thevehicle on a soil (1); at least one driving apparatus (18) for driving amicro-pile into the soil (1); and at least one punching device (19) forpunching the soil (1) in order to make a hole (2) in the soil (1);wherein: the punching device (19) in turn comprises a first member (21),and second member (22) and a first actuating device (8); the firstmember (21) is constrained to the chassis (15); the second member (22)is movable relative to the first member (21) between a first positionand a second position along a punching line; the second member (22) hasthe shape of a punch (4) with an axis of extension that extends betweena lower tip (5), insertable in the soil (1), and a top portion (6); thesecond member (22) has a cross-section that increases along the axis ofextension, going away from the lower tip (5); the first actuating device(8) is mounted between the first member (21) and the second member (22)for moving the second member (22) relative to the first member (21); themovement of the second member (22) comprising an outward stroke towardsthe second position, during which the first actuating device (8) pushesthe second member (22) towards the soil (1), applying a force on thesecond member (22) along the driving line, the second member (22) beingdesigned to apply a portion of said force to the soil (1) according to aradial line of action; the movement of the second member (22) alsocomprising a return stroke towards the first position, during which thesecond member (22) is moved away from the soil (1), and wherein: eachdriving apparatus (18) comprises a third member (23) that is constrainedto the chassis (15), a fourth member (25) that is movable relative tothe third member (23) between a first position and a second positionalong a driving line and a second actuating device (12) for moving thefourth member (25) relative to the third member (23); the movement ofthe fourth member (25) comprising an outward stroke towards the secondposition, during which the second actuating device (12) pushes thefourth member (25) towards the soil (1), applying a force on the fourthmember (25) along the driving line, the fourth member (25) beingdesigned to transmit said force to the micro-pile to be driven in; themovement of the fourth member (25) also comprising a return stroketowards the first position, during which the fourth member (25) is movedaway from the soil (1).
 12. The operating vehicle according to claim 11,also comprising a second driving apparatus for driving a secondmicro-pile into the soil (1).